Hello, all. I do a Full Backup every day of my Database. I am trying to use the previous Full backup to set up an additionnal Differential Backup, but can't do this properly... Can you suggest something? Thanks in advance

I would suggest you to do the daily backups as copy_only, so that it doesn't break the chain for transaction log backups or differential backups. After that the daily full backup won't be taken into account as basis for the differential backups.

Transaction Log backup is independent of Full / Differential backup, so neither will break the chain for TLog backups.

So you mean that 1) you are taking a differential backup, for example, in the middle of the day, based on a Full Backup taken last night?

Or that 2) each day you want to take a Differential Backup based on e.g. Last Sunday's Full backup? (i.e. and you want to take a Daily Full backup)

In the second case I can't see any benefit (i.e. having to restore using Sunday Full plus Today's DIFF as compared to just restoring Today's Full), but if I'm missing something please let me know